Peter Rabbit is 100 years old. “He doesn’t look it,” says Adrian Mitchell, whose play with music, Peter Rabbit and his Friends, opens today at the Unicorn Theatre in north London. But then, Peter has many manifestations - always in that little blue jacket and often nibbling a carrot - as a toy, in ballet, on film, decorating Wedgwood cups and plates and, of course, in the original, delicate-but-lively Beatrix Potter watercolours.

Peter also has a star role among the installations in The World of Beatrix Potter attraction at the Old Laundry in Bowness, a small town on Lake Windermere in Cumbria. It is just a few miles from Hill Top, the farm in the village of Sawrey that Potter bought in 1905. Confusingly, a centenary model, complete with birthday cake, is already on show at the Old Laundry. The reason, explains Charlotte Scott, who, with her husband, designer Roger Glossop, established the attraction 11 years ago, is that Peter has already had a 100th birthday - in 1993.

It was in 1893 that Beatrix Potter, then aged 27, invented Peter. She was writing a letter to Noel, the five-year-old son of her former governess, Annie Moore, and included drawings of Peter and his siblings. “My dear Noel, I don’t know what to write to you so I shall tell you a story about four little rabbitsI ” She subsequently turned the tale into a picture book, but it was rejected by several publishers and she had 250 copies printed privately. Then, in 1902, Frederick Warne amp; Co agreed to publish The Tale of Peter Rabbit on condition that she added coloured illustrations. The first print run, of 8,000 copies, sold out immediately. Potter had embarked on the career that made her famous and, briefly, very happy. She became engaged to one of Peter Warne’s sons, Norman, but when he died unexpectedly she was devastated.

Beatrix Potter’s determination and originality showed themselves in many ways. A passionate conservationist, she bought up large tracts of the Lake District to preserve it from development and became a leading breeder of sturdy Herdwick sheep. Having spent childhood holidays in the area, she eventually made her home in Sawrey, and in 1913, at the age of 47, she married her solicitor, William Heelis.

As a girl, living the constrained life of a Victorian young lady, Potter learned to paint, often from life. Peter and Benjamin Bunny were based on pets. She also kept mice, a rat, frogs, lizards, a bat and a hedgehog, who became Mrs Tiggy-Winkle. According to Potter, her model was very accommodating, but would yawn if propped upright for too long.

Mrs Tiggy-Winkle, inspired by a Scots washerwoman, Kathy McDonald, would have been at home in the Old Laundry, where the linen from the hotels of Windermere and Bowness used to be sent. In the story, a girl called Lucie loses her pocket handkerchiefs and finds them among Mrs Tiggy-Winkle’s washing. Now, in one of the scenes that make up the exhibition, a model of the busy hedgehog stands among the clothes washed and ironed for the other animals. Cleverly lit environments, with a soundtrack including music and even a storm, allow the visitor to wander in a magical world.

Charlotte Scott says: “We have deliberately used theatrical techniques - it’s the world we both come from.” She and Roger Glossop (who designs Alan Ayckbourn’s productions at Scarborough) head a company of stage set designers called Velvetfield, and it is they who have made the figures, including Jemima Puddleduck among the foxgloves, Mr Jeremy Fisher twirling on his lily-pad, Benjamin Bunny in his tam-o’-shanter and, of course, Peter, with Mr McGregor (whose wife cooked Peter’s father in a pie), looking quite sinister, in the background. The visitor follows lanes, peeps through windows and, perhaps best of all, walks under Squirrel Nutkins’s tree.

Meanwhile, in north London, Mrs Tiggy-Winkle, Benjamin Bunny and the house-proud Mrs Tittlemouse join Peter in Adrian Mitchell’s play - as does Potter herself. “Peter wants to be in everything,” says Mitchell. “He keeps persuading Beatrix Potter to paint him.”

By the time Benjamin’s story is told, “Peter is wiser; he has learned about Mr McGregor,” and the two rabbits rescue Benjamin’s children, the Flopsy Bunnies, from danger in the garden.

“Mr McGregor is comic and a little frightening,” says Mitchell. “When he is introduced he sings about how much he loves animals. And Peter is not the sharpest. He joins in until the verse about rabbits, when he realises just how Mr McGregor loves animals.”

This is one of 24 short songs in the production. The dialogue revels in Potter language.

“There are lovely words, like goffering, which is to do with heating irons in the laundry,” says Mitchell. “Children love to hear new words. We have kept close to the stories, but Beatrix is the link. The relationship between her and Peter comes from reading her life and learning about her relationship with animals.”

Potter’s life is also a feature at the Old Laundry exhibition. A figure of her stands stoutly beside a life-sized model of a Herdwick sheep as a film of her life story unfolds.

An animated clock, with scenes that come to life every 15 minutes, will be installed next month to mark Peter Rabbit’s publishing centenary. It is worth celebrating - 40 million copies of Peter Rabbit have been sold, in 35 languages. It has never been out of print. Here’s to the next 100 years, Peter.

Tickets and tour dates for Peter Rabbit and his Friends, the third Adrian Mitchell Potter play: 020 7609 1800The World of Beatrix Potter attraction: 015394 88444 Figures from the Royal Ballet’s The Tales of Beatrix Potter are also on show there for a limited season